From the Guidelines
The physiology of breathing is a complex process involving four key steps: pulmonary ventilation, pulmonary diffusion, transport of oxygen and carbon dioxide in the blood, and capillary gas exchange, all of which work together to supply oxygen to the muscles and remove carbon dioxide from the blood via the lungs. The process of breathing is critically related to the cardiovascular system’s capacity to supply oxygen to the muscles and the pulmonary system’s ability to clear carbon dioxide from the blood via the lungs 1.
Key Processes
- Pulmonary ventilation, or the movement of air into and out of the lungs, is the first step in this process, followed by pulmonary diffusion, which is the exchange of oxygen and carbon dioxide between the lungs and the blood 1.
- The transport of oxygen and carbon dioxide in the blood is also crucial, as it allows for the delivery of oxygen to the muscles and the removal of carbon dioxide from the body 1.
- Capillary gas exchange, or the exchange of oxygen and carbon dioxide between the capillary blood and the working muscle, is the final step in this process, and is essential for maintaining proper gas exchange and preventing the buildup of carbon dioxide in the body 1.
Regulation of Breathing
The increase in oxygen uptake by the working muscles is facilitated by an increase in cardiac output, which may increase to up to 6 times that at rest, and is also redistributed away from nonactive tissues to the skeletal muscles, which facilitates greater oxygen delivery 1. The brainstem automatically adjusts breathing rate and depth to maintain appropriate gas exchange, though we can also voluntarily control our breathing to some extent 1.
Clinical Implications
Many disease states can alter the matching of ventilation to perfusion, such as pulmonary disease, which can limit exercise by a higher than normal dead space, and chronic heart failure, which can lead to an impaired cardiac output response to exercise and a mismatching of ventilation to perfusion 1. The degree to which ventilation is abnormally heightened during exercise is directly related to the severity of disease and is a strong marker of prognosis 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Physiology of Breathing
The physiology of breathing is a complex process that involves the interaction of the central and peripheral nervous systems with the respiratory system 2. It requires the coordination of various components, including:
- Cortical (volitional) output, mainly through the corticospinal tract
- Subcortical (automatic) output, via the reticulospinal tract
- Brainstem nuclei, such as the pneumotaxic center, dorsal and ventral respiratory group, which function as rhythm generators
- Central chemoreceptors that detect changes in serum carbon dioxide and pH
Control of Breathing
The control of breathing depends on a complex feedback control system that integrates automatic and volitional aspects of ventilation 3. This system includes:
- Sensors, such as chemoreceptors and lung volume receptors, that relay information to a central controller
- A central controller, located primarily in the medulla, that integrates this information and determines the level of activation of the effectors (respiratory motoneurons and muscles)
- Inputs from suprapontine structures, including the cerebral cortex, that integrate volitional aspects of breathing into the control system
Respiratory Mechanics
Respiratory mechanics in brain-injured patients can be affected by various mechanisms, including neurogenic pulmonary edema, inflammation, and autonomic system dysfunction 4. Measurement of respiratory mechanics in these patients can help detect preclinical lung injury and guide the selection of appropriate ventilator settings to avoid ventilator-induced lung injury.
Autonomic Function
Patients with chronic obstructive pulmonary disease (COPD) often show impairment in autonomic function, which can be modulated by respiratory training techniques such as controlled breathing techniques, noninvasive mechanical ventilation, and oxygen supplementation 5. These techniques can have a positive influence on baroreceptor sensitivity and heart rate variability in patients with COPD.
Sleep and Respiratory Physiology
Respiration during sleep is determined by metabolic demand, and changes in pharyngeal dilator muscle tone, respiratory muscle tone, and body posture can contribute to hypoventilation 6. Understanding sleep-related changes in respiratory physiology can help develop new therapies to prevent hypoventilation in susceptible populations.